Recently, there is the tendency in that patients suffered from respiratory diseases such as pulmonary emphysema or chronic bronchitis have increased. One of most effective treatments for such diseases is an oxygen inhalation therapy. On the other hand, an oxygen condenser for separating oxygen-condensed gas directly from air has been developed and gradually prevailed as a treatment device for the oxygen-inhalation therapy due to the convenience when used and the easiness of maintenance.
As such an oxygen condenser, an absorption type filled with absorbent capable of selectively adsorbing nitrogen has been known. Of them, a pressure swing adsorption (SPA) type oxygen concentrator using an air compressor as means for supplying air has been used as a device for the at-home oxygen inhalation therapy. This device generally repeats, at a constant cycle, and an adsorption process for obtaining oxygen-condensed gas by supplying compressed air from a compressor to one or more adsorption beds filled with absorbent capable of selectively adsorbing nitrogen so that nitrogen is adsorbed under a pressed condition, a desorption process for desorbing the nitrogen by decreasing an inner pressure of the adsorption beds to regenerate the absorbent. If necessary, for the purpose of improving the absorbent-regeneration efficiency and rising the pressure, directly before finishing the desorption process, a pressure-equalizing process may be added wherein part of the obtained dry oxygen-condensed gas is made to reversely flow. Thus, the oxygen-condensed gas is obtained. Generally, by connecting the compressor to the fluidized bed by piping via valve means, a flow passage control for switching a pressurized air passage to the fluidized bed is carried out. Such a flow passage switching apparatus is, however, problematic in that the number of parts increases and the maintenance becomes troublesome.
To improve such inconveniences, modulated oxygen condensers are proposed wherein pressurized air is supplied to the adsorption bed via a fluid separation device having a rotary valve therein described in Japanese Unexamined Patent Publication (Kohyo) No. H7-508205 (Patent Document No. 1) and Japanese Unexamined Patent Publication (Kokai) No. 2004-209263 (Patent Document No. 2). Such oxygen condensers must be small in size when used for an at-home therapy, and thus, it is difficult to provide a sufficient space for the mechanically sealed rotary and stationary valve sections within the valve. Instead, a mechanical seal structure is adopted wherein surfaces of a rotor which is a sliding member provided on a rotary shaft side to be rotatable with the rotary shaft and a stator provided on a non-rotatable housing side, which surfaces are perpendicular to a rotary axis, are in tight contact with each other while loaded in the axial direction by pressing means such as a spring to prevent fluid from leaking out of the periphery of the shaft.
In the conventional mechanical seal, lubricant such as oil is used for decreasing the sliding resistance between the sliding surfaces. In a valve used in the oxygen condenser for switching flow passages of breathing gas, however, such lubricant could not be used. Accordingly, it has been designed so that the flatness of the sliding surfaces is extremely improved to lower the sliding resistance.